Molded phenolic compositions and process of making same



Patented Oct. 5, I926.

UNTED STATES,

PE r c GILBERT L. PEAKES, OE PERTH AMBOY, NEW JERSEY, ASSIGNOR TO BAKELITE COR PORATION OF NEW YORK, N. Y.,

A CORPORATION OF DELAWARE.

MOLDED PHENOLIC COMPOSITIONS AND PROCESS OF MAKING SAME.

No Drawing.

This invention relates to molded insulation of the type comprising a filling mate rial, or inert base, such as wood fiour, paper, fabric or the like, and an infusible phenolic resin binder; and comprises a novel product of this type characterized by a relatively high insulating value at elevated temperatures. The invention comprises also a process of heat-treating molded phenolic compositions to improve their insulating value.

The term molded phenolic compositions is used herein in a broad sense to include all such products as result from the molding of commercial molding mixtures; laminated products formed by the consolidation under heat and pressure of superposed sheets of paper, fabric or the like which have been coated or impregnated with a reactive phenolic resin; and all similar products or articles.

According to the present invention the molded phenolic composition, in the state in which it comes from the press and under the present practice is ready for the trade, that is to say, in the so-called cured condition, as distinguished from the uncured products of so-called cold-molding or quick-molding operations, in the state in which they are ready for subjection to the after-baking step,is subjected to a further heat-treatment or after-curing process, whereby its insulating quality, especially when measured at elevated temperatures of the order of 100 (3., is greatly improved. This treatment will naturally vary somewhat according to the size and nature of the article; but the conditions now preferred conditions stated are however those which,

have been found mostdesirable in practice;

and temperatures of the order of 100 C;

Application filed November 19, 1923. Serial No. 675,727.

have not been found effective even when maintained for relatively long periods.

Molded phenolic compositions to which this treatment is applicable ordinarily vary rather sharplyw-ith the temperature in their insulating quality, or dielectric strength, as measured by determining the volts per mil at which the sample will puncture when subjected to a gradually increasing voltage stress in accordance with the standard procedure of the American Society for Testing Materials; the insulating value, commonly referred to as the dielectric strength, be ing at 100 C. only a fraction, usually of the order of 10 to 25 per cent, of its value at room temperatures. An important effect of the above described heat-treatment is to, yield a product having at 100 C. a dielectric strength approximating much more closely to the dielectric strength measured at normal temperatures. Articles properly treated in accordance with this invention exhibit a dielectric strength at 100 C. which is upward of fifty per cent of their normal dielectric strength in the non-treat ed state at 20 (3., and in many cases or even 100% of this value. In exj ceptional cases higher values are observed, but this usually occurs when the dielectric strength of the untreated product is abnormally low. I 7

The eflectof the above-described heattreatment upon the dielectric strength at normal temperatures, commonly referred to as the dielectric strength-cold, is much less marked, and may even be negligible from a practical viewpoint when the molded composition has been so compounded and fabricated as to possess initially a very high oold dielectric strength. On the other hand, when the article, owing toc'auses not definitely determined, exhibits an abnormally low cold dielectric strength, the effect of the described treatment is to improve this value, raising it to or above the standard cold value. It will of course be understood that in those cases where an abnormally low cold dielectric strength is due to porosity of the article no marked improvement can be expected from the heat-treatment.

Since the molded phenolic compositions whose treatment is contemplated herein may vary widely in dielectrlc strength with variations in proportion and nature of the filler or binder, with the molding condi-' tions, as well as with many other factors, it is not practicable to give absolute average values indicating the effects of the treatment; in a typical case however a hot-press molded test sheet from a commercial black molding mixture known as #420 gave results as follows:

Betore treatment After treatment 0. 0. 0. 0'. Temp. of test 20 100 20 100 Volts per mil 505 60 550 428 In this particular case therefore the dielectric strength of the untreated material at 100 C. was about 12% of its value at guished from the so-called cold-moldin process) is upward of 150 C.; it will' e noted therefore that the preferred heattreating or curing temperature according to this invention is near the normal hot-molding tem erature. ,It is also below the .usual.

after-ha ing temperature of the cold-molding process. I

This invention is to be clearly distinguished from the after-baking step of the -so-called cold-molding or quick-molding processes,

which is applied to. uncured molded products, and

' the accomplishment of the reaction of condensation, which reaction takes place, in the hot-molding rocess, inthe res and durmg the acto molding. The eat treatment of the presentinventlonis appliedto cured s for its purpose products, meaning thereby molded products which have undergone th s condensation reaction, either during molding or subsequently thereto.

I claim 1.Process of heat-treating molded phenolic compositions to improve their insulating quality comprising subjecting the molded cured product to predetermined prolongedheat-treatment ata temperature be low the normal molding temperature.

2. Process of heat-treating molded phe- 0 nolic compositions to improve their insulating quality comprising subjecting the molded cure-d product to predetermined prolonged heat-treatment at a temperature of about 125135 C.

3. Process according to claim 1 in which the molded cured product isheat-treated at about 125 135 C. for at least 48 hours.

. .4. As a .new article of manufacture, a molded phenolic composition having a dielectric strength measured at 100 C. which is at least fifty percent of the dielectric strength of the same material measured at 20 C.

5. As a new article of manufacture, a molded phenolic composition having a dielectric strength measured at 100 C. which is at least seventy percent of .the dielectric stren th of the same material measured at 6. As a new article of manufacture, a laminated article having a phenolic resin binder, said article possessing a dielectric strength measured at 100 C. which is at least fifty percent of the dielectric strength of the same material measured at 20 C.

7. As a new article of manufacture, a

laminated article having a phenolic resin binder, said articlepossessing a dielectric strength measured at 100C. which is at least seventy percent of the dielectric strerbgth of the same material measured at 20 *In testimony whereof, I afiix my signature. 7 GILBERT L. PEAKES. 

